The invention relates to improvements in a butterfly valve for the control of gaseous fluids, comprising a valve disc having an annular sealing surface near its periphery, a flat annular valve seat provided in a housing accommodating the valve, and actuating means for opening and closing the valve.
Butterfly valves are routinely employed for the control of gaseous fluids in services for which some degree of leakage can be tolerated across the valve. The propensity of such valves, particularly the larger valves often having a diameter of one meter or more, to provide a less than leak-proof seal is well known. For instance, Great Britain patent 901,607 recognizes that leakage is a problem and provides a means for its detection.
In a variety of industrial applications, however, it is absolutely necessary that leakage past a valve be prevented. For instance, such is the case when there is a danger of the escape of a toxic substance or when an undesirable reaction occurs between two different fluids separated by the valve. The latter situation often arises in regenerative processes in which there is a periodic switching between utilization of two or more different treating fluids. It is an object of this invention to provide a butterfly valve suitable for leak-proof services in applications such as these.
Commonly-assigned copending application bearing Ser. No. 769,811 and filed Feb. 17, 1977, provides a solution to the leakage problem associated with the use of butterfly valves according to which a double seal is provided between valve disc and valve seat. A purge fluid under high pressure is injected into the space between the two seals to provide a barrier to leakage across the valve. This approach to solving the leakage problem is applicable both in a valve with an annular sealing surface near the periphery of the valve disc cooperating with a flat annular seat, as well as in a valve with a circumferential seal between the periphery of the valve disc and an accommodating seat. In the latter of these two butterfly valve types, to which the copending application is particularly directed, the employment of purge fluid at the seal is generally preferred over the use of resilient seat materials as is illustrated by Great Britain Pat. No. 901,607 and U.S. Pat. No. 2,705,016. However, in many applications of butterfly valves to the control of gaseous fluids, it is undesirable to utilize a purge fluid type of seal, as, for instance, where the purge material introduces a source of contamination to the fluid on either side of the valve disc. The nature of the gaseous fluids contained by the valve and the processing to which these fluids are subjected often dictates that inert purge gases be used which are only obtainable with great expense and inconvenience.